It is known that in conjunction with a face-to-face weaving loom a Jacquard machine ensures that the various pile warp threads are placed in the correct position before each pick, so that the fabric is woven according to the desired weave, with the desired patterns.
Such Jacquard machines comprise at least two rows of hooks and two knives constantly moving up and down in counterphase opposite each row of hooks, which knives can carry along the hooks of that row, while each hook as desired can be held by a selection mechanism or otherwise in its top or bottom position (depending on the design of the Jacquard machine), for the duration of one or more cycles of the knives.
Two of such rows of hooks are called complementary rows of hooks, and two hooks situated directly opposite each other, each belonging to one of two complementary rows of hooks, are known as a complementary set of hooks. The hooks of one or two complementary sets of hooks, through the interaction imposed by interconnection of said hooks, lifter rollers, lifter cords placed around said rollers, and warp threads connected to a lifter cord, can move one or more warp threads (by means of a harness cord) to various heights, as a result of the different positions of the interacting hooks. In other words, by selecting or not selecting each of the hooks which interact with the same lifter mechanism, the warp threads connected to a lifter cord of said lifter mechanism can be moved into the desired position before each pick, in order to produce a face-to-face fabric. This principle is known and is illustrated with reference to the example which follows, in which reference is made to the appended FIG. 1.
For weaving certain weaves in face-to-face fabrics, it is necessary that in two successive picks the pile warp threads can be placed in three possible positions relative to the weft threads in top fabric and bottom fabric: above said weft threads, below said weft threads, and between said weft threads. These are known as the positions Above, Below and Middle respectively. For achieving these three selection possibilities, use is made of three lifter elements (1), (2), (3) (see FIG. 1). Each lifter element is composed of two rotary rollers (1', 1"), (2', 2"), (3', 3") situated above one another.
The two hooks of two sets of complementary hooks (9), (10) and (9'), (10') are connected by a downward-hanging lifter cord (7), (8) respectively, while the downward-hanging part is passed round under the top roller (1') of the lifter element (1) and under the top roller (2') of lifter element (2) respectively.
A lifter cord (6) is connected by one end in a fixed point lower down than the rollers (1") and (2"), is guided over the roller (1") of lifter element (1), has a downward-hanging part which is passed under the top roller (3') of lifter element (3), and is finally guided over the roller (2") of lifter element (2) and fixed by the other end in a fixed point situated lower down.
Lifter cord (4) runs over the bottom roller (3") of the bottom lifter element (3) and is connected by one end lower down, by means of the harness cord, to one or more pile warp threads, and is connected by the other end to a fixed or movable (controllable) point or grate (5).
If none of the four hooks is selected, then hook (9), on the one hand, moves up and down in counterphase with hook (10), and hook (9'), on the other hand, moves in counterphase with hook (10'). The lifter elements (1) and (2) consequently remain at the same height. No lift takes place, and the pile warp threads remain in the "below" position.
If one of the hooks, for example hook (9), is selected in its top position, after hook (10) is raised by the knife (over a height h) the lifter element (1) is raised over a height h/2. Lifter element (2) is not raised, since neither hook (9') nor hook (10') were selected. The lifting of lifter element (1) over a height h/2 results in the same lift (over height h/.sub.2) of lifter element (3), as a result of which the pile warp threads are raised over a height h. They are taken into the "middle" position. When hook (10) is in its lowest position, the warp threads are in the "below" position.
If one hook (e.g. (9) and (9')) of each set of complementary hooks is now selected in its top position, then both lifter elements (1) and (2) are raised over a height h/2 when the complementary hooks (10) and (10') are raised. This results in a lift over a height h of lifter element (3), as a result of which the pile warp threads are raised over a height 2h. They are taken into the "above" position. When the hooks (10), (10') are moved into their lowest position, the pile warp threads are in the "below" position.
Through the different selection possibilities of the hooks and through moving the grate (5) to a different level, possibly together with one of the hooks, the pile warp threads can be taken into three possible positions on two successive picks.
The great disadvantage of this known lifter mechanism lies in the fact that two complementary sets of hooks (9, 10), (9', 10') are necessary, which results in a bulky and expensive machine.
This disadvantage is eliminated by the lifter mechanisms which are disclosed in Belgian Patent No. 09000559, filed on 31 May 1990.
It relates to a lifter mechanism for a Jacquard machine, to which only one set of complementary hooks need be connected, and by which selection or non-selection of these hooks provides the possibility of placing the warp threads in 3 possible positions for each 2-shot pattern repeat.
The abovementioned patent describes two possible embodiments which are illustrated in the appended FIG. 2. In a first embodiment, one end of a downward-hanging lifter cord (13) is fixed to each of two complementary hooks (11), (12). This lifter cord (13) is passed round the top roller (14') of a lifter element (14). Fixed to one of the hooks (11), (12) is the end of a second lifter cord (15), which hangs down lower than the lifter element (14) and is passed below the top roller (17') of a lifter element (17) and is then taken back up and runs over the bottom roller (14") of lifter element (14) and is connected to a fixed or controllable grate (16) back down lower than said roller (14"). Over the bottom roller (17") of this lifter element (17) lies a third lifter cord (18) which is connected by one end lower down to one or more pile warp threads (by means of harness cords), and is connected by the other end lower down than the bottom roller (17") of the lifter element (17) to a fixed or controllable grate (19).
In the second embodiment, the top lifter element (14) is fixed to one of the two complementary hooks (11) and (12), while another lifter cord (21) is connected by one end to the other hook (12), lower down than lifter element (14), is passed under the top roller (17') of a lifter element (17), and runs back up, is placed over the bottom roller (14") of lifter element (14) and is connected back lower down by the other end to a fixed or controllable grate (16). Over the bottom roller (17") of lifter element (17) runs a lifter cord (18) which is connected by one end--lower down--by means of harness cords to the pile warp threads, and is connected by the other end--also at a lower level--to a fixed or controllable grate (19).
If hook (11)--or (12)--is selected in its top position and the grates (16), (19) are assumed to be fixed, then the warp threads--after the raising of the other hook (12) or (11)--are raised over a height 2h and move from the "Below" position to the "Above" position.
If no hook at all is selected, the warp threads are raised by lifting hook (11) over a height h and taken from the "Below" position to the "Middle" position.
If the mechanism is now provided with means by which one of the grates (for example, grate (16)) is raised by knife (12') together with hook (12) over a height h, after the lifting of hook (12) the warp threads go a distance h lower than was the case with fixed grate.
For a more detailed description of all possibilities of these known lifter mechanisms, we refer you to Belgian Patent No. 9000559.
The lifter mechanism indicated above is a solution for generating three positions for the pile warp threads with only two complementary hooks and two lifter elements and two grates.
A disadvantage of this solution is, however, that two lifter elements and two grates (16), (19) are necessary, with the result that the whole machine takes up a large amount of space vertically, so that Jacquard machines provided with this lifter mechanism have to be set up at a very high level, in order to obtain acceptable angles of incidence of the harness cords in the harness cord board.